When a cardiotachometer is used in a hospital for the monitoring of critically ill patients in intensive care units, it is important that information be proided as soon as possible after connecting the cardiotachometer to the patient and it is further important that the information provided be as accurate as possible. In calculating a heart beat rate, it is preferable to count heart beats for at least one full minute to minimize the effect of error due to occasional noise in the electrical system or spurious heart beat signals. Calculating a rate in beats per minute based on a count during fractions of a second multiplies any error in the count. Yet, 1 minute is frequently too long to wait for a doctor to get the first information from the cardiotachometer.
Accordingly, it is a major purpose of this invention to provide a cardiotachometer which is versatile in that it meets both of these objectives in that it provides a reading as quickly as possible while then providing a more accurate reading after a minute has passed.
Because these caridotachometers are used for relatively long term monitoring purposes, it is also a purpose of this invention to provide a cardiotachometer which will provide regular, continuous and automatic updating of the heart beat rate. It is important that this updating occur more frequently than once a minute so that any sudden change in the patient's heart beat will be noticed and an appropriate warning signal can be actuated.
At the same time, it is important that the updating be in accordance with a routine which will minimize the effect on the output heart beat rate of a noise spike.
In any monitoring operation, it is important that the measurement data provided be relatively unambiguous and that its significance not be subject to misinterpretation or misunderstanding. Accordingly, it is an important purpose of this invention to provide an unambiguous readout in a device which also provides the dual function of a relatively speedy readout as well as an ultimately accurate readout.
In order to provide the benefits of versatility and unambiguous presentation in a context that will be used as widely as possible, it is a further purpose of this invention to meet these objectives in a device that is relatively simple, reliable, easy to maintain and inexpensive.
Patents illustrating known cardiotachometer techniques are U.S. Pat. Nos. 3,202,149, 3,603,769, 3,773,038 and 3,807,388.